ESP32-PRO new IoT board with 4MB external RAM, 4MB external Flash, external crypto engine, LiPo charger


What you see above is our attempt to make ESP32 board with 4MB RAM. Reading the ESP32 datasheet this is quoted as the maximum possible external RAM possible to attach.

It’s named ESP32-PRO and here is the Github repo for it.

We encounter lot of problems while designed it, thanks to Rudi from for the tips and help. As there is the usual mess with the documentation and lot of unclear stuff.

We saw in the new WROVER-KITS we got that the module which is used is not WROOM, but WROVER and inside it has pSRAM.

The pSRAM is working on 1.8V and share same data pins as the Flash so we had to find 1.8V Flash also.

Another issue is that in the documentation pSRAM clock and data are reversed for unknown reason, but at least the software which run on WROVER module has these correctly set 🙂 so we had to ignore the Espressif datasheet and user manual info.

On top of this in the documents never mention that GPIO12/MTDI must be pull high if the power supply is 1.8V neither their reference design show this.

At least now having OSHW board with all correct settings will help other to not struggle all obstacle like us on the road to add external RAM.

We had to go to bare ESP32 chip as the RAM signals are not available on WROOM neither WROVER modules, this will lead to paid certification which we still do not know how much will be, but will have to add to the sale price of this module, so price is yet unknown but will be fair 🙂

As Rev.0 of the ESP32 chip has issue with cache for external RAM, we try to communicate with Espressif if we have to expect other bugs and issues with Rev.1 using external pSRAM, will keep you updated.

Beside the ESP32 we add PIC32MX270F256DT, this is nice processor with USB-OTG which will allow ESP32 to connect to both USB hosts and to act as USB-host and read for instance external USB Flash or take pictures from USB Webcam etc.

Why not AVR? Because AVRs are in trap of their own success. For the price of PIC32MX270F256DT which has 64K RAM, 256K Flash and USB-OTG you can buy ATMega32u4 which has only 2K RAM and 32K Flash and just USB device.

PIC32MX270F256 opens much more possibility with plenty of Flash and RAM.


15 Comments (+add yours?)

  1. CSDexter
    Jun 21, 2017 @ 17:53:28

    What crypto engine do you have in mind? Or will the PIC32 also run the crypto code?


  2. Anton Shmagin
    Jun 22, 2017 @ 04:44:51

    I want this board ASAP.
    This is awesome!!!


  3. Sprite_tm
    Jun 22, 2017 @ 05:21:43

    Next time you’re having issues, feel free to contact Espressif directly as well, either using mail or on At least amongst the engineers, there’s a fair amount of love for open-hardware boards, and we wouldn’t mind at all helping you with issues encountered while designing them.

    (And what’s with the external crypto engine, by the way? Did you encounter issues doing ECC/ECDSA on the ESP32 itself?)


    • OLIMEX Ltd
      Jun 22, 2017 @ 08:15:14

      I see you are from Espressif. Can you give me contact for technical support? I have emailed John Lee about the pSRAM issues and he never reply back. Why the documentation is not corrected, why the schematic of WROVER kit on Espressif site still miss pullup resistor and swapped clock and chipselect for the pSRAM? obviously this is not working schematic, why you are misleading your customers? I’m sure you guys are busy with certifications etc, but we try to help by making OSHW reference design and you are leaving us on our own.


    • rudi ;-)
      Jun 22, 2017 @ 11:09:05

      you did it really – 😉 great! well done!
      where i can order?

      best wishes
      rudi 😉


  4. Toto
    Jun 23, 2017 @ 13:38:46

    What is the serial RAM used with 4MByte size ? I see LY68S3200SLT in the schematic but when googling this ref I get no result ?


  5. SK
    Jun 24, 2017 @ 13:04:26

    AES-256 keys sniffed in seconds using €200 of kit a meter away:


  6. bvernoux
    Jul 08, 2017 @ 10:22:41

    For information ATECC508A have not a full datasheet/ref manual (just a ATECC508A – Summary Datasheet) and requires to sign a NDA for the complete datasheet, so I think it is not very good to use this CryptoAuthentication chipset …


    Sep 01, 2017 @ 14:54:42


  8. Barbara Potter
    Feb 18, 2019 @ 17:57:30

    Rudi. To talk about security in IoT M2M you should know the difference between IoT and M2M


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